Adam Peaty won gold and Jazz Carlin claimed a silver as Great Britain secured their first medals of the 2016 Olympics on day two in Rio.Peaty, 21, smashed his own world record to win the 100m breaststroke in 57.13 seconds and end GB's 28-year wait for a men's Olympic swimming title.
Minutes later, Carlin won silver in the women's 400m freestyle.
In the tennis, Novak Djokovic was knocked out in the singles, while Andy and Jamie Murray exited the doubles.
It was another day of incident and drama in Brazil:
- Cycling crash - Britain's Lizzie Armitstead was fifth in the women's road race won by Anna van der Breggen after leader Annemiek van Vleuten suffered a horrific crash.
- Tennis turn-ups - Djokovic was undone by Juan Martin del Potro, the Murray brothers lost to unseeded Brazilians and three-time champions Serena and Venus Williams were beaten in the women's doubles.
- Phelps wins 19th gold - Michael Phelps won a record 19th Olympic gold as the United States clinched the men's 4x100m freestyle relay.
- First gold for Kosovo - Majlinda Kelmendi became Kosovo's first Olympic medallist, winning the women's -52kg judo.
Swimming champion who was scared of waterPeaty had a fear of water as a young child but is the first British man to win Olympic swimming gold since Adrian Moorhouse in 1988.
"I did it for my country and that means so much for me," the City of Derby swimmer told BBC Sport after victory watched by parents Caroline and Mark.
The world, European and Commonwealth champion completed a full set of titles as he led from the start with a blistering performance that left him more than 1.5 seconds clear of the field.
He began the Games as the world record holder with a time of 57.92 and has lowered it by 0.79, having also set a mark of 57.55 in his opening heat.
After earlier near-misses for fencer Richard Kruse and swimmer Hannah Miley, victory brought Britain's first medal of Rio 2016.
Within minutes, there was another medal on the board thanks to Carlin, who took silver as the USA's Katie Ledecky won in a world-record time.
The 25-year-old Welsh swimmer held off American Leah Smith in the final 50 metres to claim second.
"I can't believe it. I'm on the edge of tears," said Carlin, who missed out on selection for the London 2012 Games.
"I was in the pool room watching Adam and I had goosebumps on the block.
"To see your team-mate achieve a new world record and become Olympic champion right before you swim definitely got me pumped up."
Britain ended day two of the Games in eighth place in the medal table, which is topped by the United States, ahead of China and Australia.
Phelps makes history - and so do KosovoPhelps arrived in Brazil as the most decorated Olympian in history and has now won 23 medals at five Games.
The 31-year-old, who came out of retirement in 2014, swam the second leg for the USA in their relay triumph.
"On the block, I thought my heart was going to explode," said the record-breaking star. "I was so hyped, so excited."
Elsewhere in the pool, Russian Yulia Efimova, a convicted drug cheat, was again booed before and after winning her semi-final in the 100m breaststroke.
Tearful Majlinda Kelmendi put Kosovo on the medal board for the first time in its history by winning judo gold.
The disputed Balkan territory, which declared independence from Serbia in 2008, is making its Olympic debut.
Double world champion Kelmendi, 25, overpowered Italy's Odette Giuffrida. Having represented Albania at London 2012, Kelmendi had told the BBC before the Games: "I just wanted to show the world we need to be equals."
Meanwhile, China's Wu Minxia became the first diver to win five Olympic golds by winning the women's 3m synchronised springboard with Shi Tingmao.
Leader crashes in women's road raceDutch cyclist Van Vleuten suffered severe concussion and three small fractures in her lower back after a shocking crash in the road race.
She had pulled clear with 10km to go but came off her bike on a sharp turn while travelling at speed down the Vista Chinesa descent.
The 33-year-old lay motionless while help arrived and there was widespread concern for her well-being, but she later tweeted that she would be fine, revealing she was in hospital with "some injuries and fractures".
After only been cleared to compete earlier this week after winning an appeal over a missed drugs test, British cyclist Armitstead ended a turbulent week by finishing just outside the medals.
The Brits - the best of the restFencer Kruse eyed Britain's first Olympic medal in 52 years, but lost 15-13 to Russian Timur Safin as they fought for bronze in the men's foil.
The remarkable story of eventer William Fox-Pitt continues. Ten months after being in an induced coma after a fall, he remains in the gold medal position after the completion of the dressage, with the cross-country and showjumping disciplines to come.
Britain survived a scare in the women's gymnastics as Ellie Downie was injured after falling on her neck during her floor routine. She later returned to help her team qualify for the final.
Andy Murray may have lost in the doubles, but he started his singles defence with a 6-3 6-2 win over Serbia's Viktor Troicki, while 10th seed Johanna Konta also went through in the women's event, beating Stephanie Vogt 6-3 6-1.
AnalysisTom Fordyce, BBC's chief sports writer:
"After the disappointments earlier in the day - Kruse going so close, Armitstead not getting close enough, the Murray brothers crashing out - 15 minutes close to midnight in the Aquatic Centre changed it all for Britain.
"Four years ago, GB swimmers won just one silver and two bronze medals in the entire Games. In 12 glorious minutes here in Rio, Peaty and Carlin gave them a gold and silver.
"Even in London, Team GB didn't start so well. By the end of day two in 2012, the haul was two silvers. Britain's 2016 Olympics are up and away."
Shocks on the tennis courtWorld number one Djokovic was in tears after going down 7-6 (7-4) 7-6 (7-2) to Argentine Del Potro.
The 29-year-old Serb has won four out of the past five Grand Slams, but also suffered a surprise early exit at Wimbledon last month.
Murray and brother Jamie were knocked out in the first round by unseeded Brazilians Thomaz Bellucci and Andre Sa.
The Olympic winning run of Serena and Venus Williams also came to an end.
Winners of the women's doubles in 2000, 2008 and 2012 - they did not compete together in 2004 - the American siblings suffered a surprise 6-3 6-4 loss to Czech pair Barbora Strycova and Lucie Safarova.
Doping controversy continues and weather woesWhile more than 270 Russians compete at the Olympics, the country won't be represented at the Rio Paralympics next month.
The Russian Paralympic Committee says it will appeal against the blanket ban, which follows claims of state-sponsored doping.
Olympic rowers were left frustrated when competition on day two was postponed because of high winds.
Monday's action sees Britain's Helen Glover and Heather Stanning begin their defence of their pairs title from 16:30 BST
And on to day three...There are 14 gold medals on offer, with British interest in the men's team gymnastics final from 20:00 BST.
The first Olympic rugby sevens final will be held from 23:00 as the women's contest reaches its climax. GB take on New Zealand in the last four (19:00).
And British diver Tom Daley will make his first appearance of Rio 2016 in the men's 10m synchro diving competition, which begins at 20:00.